A variety of methods for computerized score following have developed over the past few decades. “Score following,” in the context of the present patent application, means analyzing, in real-time, audio input resulting from a performance of a piece of music, and automatically tracking the corresponding location in the musical score of the piece. (The term “audio input,” as used in the context of the present patent application and in the claims should be understood broadly to encompass any and all forms of audio signals, including digital audio data signals, such as Musical Instrument Digital Interface (MIDI) data streams.) Reliable score following is complicated by the fact that performers often change tempo, make mistakes, or otherwise play the music not exactly as it is written.
Various methods of score following have been described in the patent literature. For example, U.S. Pat. No. 5,913,259, whose disclosure is incorporated herein by reference, describes a computer-implemented method for stochastic score following. The method includes the step of calculating a probability function over a score based on at least one observation extracted from a performance signal. The most likely position in the score is determined based on the calculating step.
Some recent efforts in score following have focused on the use of Hidden Markov Models (HMMs). A HMM is a statistical model in which the system being modeled—in this case, the performance of a musical piece—is taken to be a Markov process with states that are not directly observable (“hidden”), but which give an observable output. A probabilistic analysis is applied to the observed output in order to infer the sequence of states traversed by the system. Jordanous recently surveyed the application of HMMs to score following in a presentation entitled “Score Following: Artificially Intelligent Musical Accompaniment” (University of Sussex, 2008), which is incorporated herein by reference.